From the World Heritage inscription:
The massive White Tower is a typical example of Norman military architecture, whose influence was felt throughout the kingdom. It was built on the Thames by William the Conqueror to protect London and assert his power. The Tower of London – an imposing fortress with many layers of history, which has become one of the symbols of royalty – was built around the White Tower.
The Tower of London is perhaps the largest tourist trap of all the World Heritage sites I’ve visited. It is worthy of being on the list, but they really sock it to you with the entrance fee and all the other touristy stuff surrounding it.
View my complete list of UNESCO World Heritage Sites